Hi Norm, I am not sure if your questions have already been answered by the list but let me make an attempt anyway.
You asked : "would you please address the issue of connecting (or not connecting) the ac neutral to earth." IMO not connecting the ac neutral to earth would make the electrical system safe for the user making accidental contact with a hot conductor. However if the user begins to ignore the basic safety rules and becomes complacent about touching hot conductors he/she will be at the mercy of the system being fault free. Therefore a system with an isolated neutral ought to be checked frequently (preferably automatically) to verify all the current carying conductors are indeed isolated from the chassis. Another shortcoming of the ungrounded neutral is you cannot use GFCI circuit breakers. One other shortcoming may be the increased vulnerability of your electronics to lightning. The isolation transformer that is providing the floating secondary neutral should be shielded (preferably both primary and secondary shields) and the shields should be hardwired to earth. You asked : "I believe in the US power that comes into a house is from a center tapped secondary winding in the pole transformer which delivers 240 vac at the ends of the coil and the neutral comes from the center tap. The grounding of the neutral is only added in the house's breaker box by the neutral/grounding jumper wire. Correct me if I am mistaken." Correct, except I have never seen a jumper wire. The panels usually have a long aluminum block bolted to the chassis and it has a bunch of screw terminals for both neutral and ground wires. US house wiring code requires both neutral (white) and ground (green) wires to be terminated to the chassis of the distribution panel/circuit breaker box. The chasis of the distribution panel is also routed (with a green wire) to a ground rod or a buried water pipe. I remember some Canadian folks on the list freaking out when they heard white neutral and green ground wires are bonded at the chassis of the panel but this is the way it is, and it makes sense to us. You asked : "I seem to have read that the European electrical system has ungrounded neutrals. Is this true or not?" In Turkey the houses are wired to one phase of the 220V Wye pole transformers with a pair of copper wires. One wire is hot and it has insulation, the other wire is the neutral and it is a bare copper conductor. The bare wire is bonded to the steel pipes that bring water to the house. The metal surfaces of the appliances are bonded to the bare neutral with a jumper and this jumper may be opened by the electrician to test the appliance for leakage. I believe the newer houses are using an insulated neutral and a bare ground wire so that GFCI devices can be used. The chassis to neutral jumper on the appliances are removed to be able to use the GFCI devices in bathrooms. Cheers Ahmet From: [email protected] To: [email protected] Date: Wed, 8 Dec 2010 23:05:56 -0500 Subject: Re: [Liveaboard] GALVANIC ISOLATOR Ahoy Al, I understand the wisdom of connecting all the touchable metal parts of electrical equipment to ship's earth so the bilge water and all touchable metal parts will be at the same voltage as the earth and I do this on my vessel. It is also a good idea to have a way to measure the ac voltage/current between the grounding (green or bare) wires coming from your system, and the grounding point to which you attach them, so you can be aware of any leakage. But would you please address the issue of connecting (or not connecting) the ac neutral to earth. For example, my 240 vac loads (and those ashore) have no neutral. Why should 120 vac loads be any different? Wouldn't it make things safer to isolate *all* current-carrying conductors rather than connect neutral ( a current carrying conductor) to the ship's hull or other similar earth-like structure? I seem to have read that the European electrical system has ungrounded neutrals. Is this true or not? I believe in the US power that comes into a house is from a center tapped secondary winding in the pole transformer which delivers 240 vac at the ends of the coil and the neutral comes from the center tap. The grounding of the neutral is only added in the house's breaker box by the neutral/grounding jumper wire. Correct me if I am mistaken. I have had an ungrounded neutral 120 vac system for 30 years on an electrically powerful and complex vessel and have never felt the slightest tingle. I did this mainly because that was the way they did it on the many merchant marine ships I served on and because I believed the safety aspects of this scheme would work just as well on my own vessel. Norm S/V Bandersnatch Lying Julington Creek FL N30 07.68 W081 38.47 ----- Original Message ----- From: Al Thomason To: [email protected] Sent: 12/8/2010 9:03:06 PM Subject: Re: [Liveaboard] GALVANIC ISOLATOR Hi: OK, in short I think there are two questions here: 1) Connect the onboard AC safety ground to the onboard DC Ground point: Yes – always. There has been several articles over the years on people dying when swimming around a faulty boat w/o this connection. ABYC requires it. Some will complain that this can cause issues with stray current and galvanic issues, but bottom line: This bonding is a major safety issue, the other concerns can be addressed below. And more so, if something does go very very bad, and you do not have this on your boat can cause lots of problems for you. Here is an article of a local boy who died as a direct result of the boat not having this connection and a fault occurring: http://www.abycinc.org/lucas_ritz.pdf 2) Connecting of ships AC Safety Ground to Shore Safety Ground.: There are basically two ways to do this: 1) make the connection via your shore power cable - use of a galvanic Isolator can help reduce some of the stray current concerns here. And 2) use a true isolation transformer. In this case, the shore safety ground is only connected to the shield in the transformer, and then a new bonding point is established by connecting the ship safety ground and ship neutral onboard (and after the isolation transformer). This approach will remove almost all issues with stray currents. This is not really that complex of a topic, though some folks like to poke at #1 and cause confusion. Note also that the above might be modified some for non US boats (e.g. EU boats). I am just not sure the best practice for them and the AC system can be slightly different then the US system. (Beyond 120v/60hz..) Good luck! -al- From: [email protected] [mailto:[email protected]] On Behalf Of Emory Jones Sent: Wednesday, December 08, 2010 4:30 PM To: [email protected] Subject: Re: [Liveaboard] GALVANIC ISOLATOR Thanks to all who responded! There does not seem to a consensus in regard to the AC ground. Any other (additional) discussion would certainly help to educate me. I am concerned about an AC to DC connection however my fears may be ungrounded (sorry I couldn't resist). Thanks again for all the input. Emory Jones S/V Jacob Andrew Solomons, MD _______________________________________________ Liveaboard mailing list [email protected] To adjust your membership settings over the web http://liveaboardonline.com/mailman/listinfo/liveaboard To subscribe send an email to [email protected] To unsubscribe send an email to [email protected] The archives are at http://www.liveaboardonline.com/pipermail/liveaboard/ To search the archives http://www.mail-archive.com/[email protected] The Mailman Users Guide can be found here http://www.gnu.org/software/mailman/mailman-member/index.html
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